1. Technical Field
The present invention relates to an image display device and a light source device.
2. Related Art
In recent years, while demands for downsizing of projectors are growing, in accordance with increase in output power of semiconductor lasers and appearance of blue semiconductor lasers, projectors or displays using laser light sources have been considered. Since the wavelength band of the light source is narrow, these devices can provide remarkably wide color reproduction range, and it is possible to downsize the devices and to eliminate composing elements thereof, thus the devices have great potential as display elements for the next generation.
As the light sources used for an image display device, three colors of laser light sources, namely R (red), G (green), and B (blue) laser light sources are required. Although original resonance for R and B can be realized by semiconductor lasers, there is no original resonance for G. Therefore, it has been considered to utilize the second harmonic wave generated by inputting an infrared laser beam to a nonlinear optical element (wavelength conversion element: SHG) (see, for example, JP-A-2001-267670).
Here, in an illuminating method used for the image display device equipped with a laser light source, grayscale is expressed by pulse width modulation or intensity modulation (see, for example, JP-A-8-24077). In an image projection system described in JP-A-8240779, a control circuit determines and controls the intensity variation of the light source so as to be synchronized with a data input signal to DMD.
However, if the pulse width modulation or the intensity modulation is used as in the related art described above, it becomes necessary to increase duty ratio of the laser beam pulses emitted from the light source or to increase the intensity of the laser beam converted by the wavelength conversion element in order for displaying bright images. This problematically shortens a life of the light source device. If the intensity of the laser beam is decreased to avoid this, the light density of the incident light to the wavelength conversion element decreases, and accordingly the wavelength conversion efficiency problematically decreases. Meanwhile, if the intensity of the laser beam is decreased in the case of the intensity modulation, the wavelength conversion efficiency of the wavelength conversion element problematically decreases in the same way.